Hexachlorocyclopentadiene

77-47-4

Hazard Summary-Created in April 1992; Revised in January 2000

Hexachlorocyclopentadiene is an intermediate in the manufacture of some
pesticides. Hexachlorocyclopentadiene isvery toxic following
acute (short-term) oral and inhalation exposures. The chemical is
a severe eye, skin, and pulmonary irritant in humans, with effects including
tearing of the eyes, sneezing, salivation, blistering, burns, and cough
from acute exposures. Limited information is available on chronic
(long-term), reproductive, developmental, and cancer effects of hexachlorocyclopentadiene
in humans. Animal studies have seen effects on the lung, liver,
kidney, and blood. EPA has classified hexachlorocyclopentadiene
as a Group D, not classifiable as to human carcinogenicity.

Uses

Hexachlorocyclopentadiene is the key intermediate in the manufacture
of some pesticides, including heptachlor, chlordane, aldrin, dieldrin,
and endrin. (5,6)

Hexachlorocyclopentadiene is also used in the manufacture of flame
retardants and some resins and dyes. (1,8)

Sources and Potential Exposure

Workers involved in the manufacture of hexachlorocyclopentadiene
and during the manufacture of products containing the chemical would
have the highest exposure to hexachlorocyclopentadiene. (1,9)

Hexachlorocyclopentadiene has been detected at low levels in ambient
air. The sources of the chemical in air appear to be releases
from manufacturing processes or incineration and landfilling of wastes
containing hexachlorocyclopentadiene. (1)

Assessing Personal Exposure

Laboratory tests can detect hexachlorocyclopentadiene in blood or
urine. (1,9)

Health Hazard Information

Hexachlorocyclopentadiene is a severe eye, skin, and pulmonary irritant
in humans. Inhalation of the chemical causes tearing, sneezing,
and salivation, and skin contact can cause blisters and burns. (1,3)

The major target organ for acute hexachlorocyclopentadiene toxicity
is the lung, with cough, chest pains, and difficulty in breathing reported
in humans. Nervousness, headaches, and abdominal cramps are other
symptoms reported from hexachlorocyclopentadiene toxicity. (1,3)

Tests involving acute exposure of rats have shown hexachlorocyclopentadiene
to have extreme toxicity by inhalation
exposure, moderate toxicity by oral
exposure, and high to extreme
toxicity by dermal exposure. (3,4)

Chronic Effects (Noncancer):

Epidemiologic studies on workers have not shown any significant differences
in mortality between workers exposed to hexachlorocyclopentadiene and
those in the general population. However, these studies are limited
by short follow-up periods, lack of data on cigarette smoking, and other
factors. (1,2)

Chronic exposure to hexachlorocyclopentadiene, via inhalation, has
been studied in animals, with effects noted in the lung, liver, kidney,
and blood. (1,3,9)

EPA has established a Reference Concentration (RfC)
of 0.0002 milligrams per cubic meter (mg/m3) for hexachlorocyclopentadiene,
based on respiratory effects in rats. (2)

The Reference Dose (RfD)
for hexachlorocyclopentadiene is 0.006 milligrams per kilogram body
weight per day (mg/kg/d) based on stomach lesions in rats.

The RfC and RfD are not direct estimators of risk but rather reference
points to gauge the potential effects. At exposures increasingly
above these levels, the potential for adverse health effects increases.
Lifetime exposure above the RfC or RfD does not imply that an adverse
health effect would necessarily occur. (2)

Reproductive/Developmental Effects:

No information is available regarding the reproductive or developmental
effects of hexachlorocyclopentadiene in humans. (1,3,9)

Animal studies have not reported birth defects from exposure to hexachlorocyclopentadiene
by gavage (placing the chemical experimentally in the stomach), and
no information is available regarding reproductive or developmental
effects from inhalation exposure. (1-3)

Cancer Risk:

As discussed above in the chronic effects section, epidemiologic
studies have not demonstrated any differences in mortality between hexachlorocyclopentadiene-exposed
workers and the general population. The observed mortality included
deaths from cancer, as well as from other diseases. (1,2)

The National Toxicology Program (NTP) completed a 2-year inhalation
study and concluded that there was no evidence of carcinogenic activity
in rats and mice. (5)

EPA has classified hexachlorocyclopentadiene as a Group D; not classifiable
as to human carcinogenicity. (2)

Physical Properties

Hexachlorocyclopentadiene is a pale-yellow liquid with a characteristic
pungent, musty odor; the odor threshold is 0.03 parts per million (ppm).
(1,7,8)

The chemical formula for hexachlorocyclopentadiene is C5Cl6,
and it has a molecular weight of 272.29 g/mol. (1,8)

The vapor pressure for hexachlorocyclopentadiene is 0.08 mm Hg at
25 °C, and the log octanol/water partition coefficient (log Kow)
is 5.04. (1,8)

Health Data from Inhalation Exposure

ACGIH TLV--American Conference of Governmental and Industrial
Hygienists' threshold limit value expressed as a time-weighted average;
the concentration of a substance to which most workers can be exposed
without adverse effects. LC50 (Lethal Concentration50)--A calculated
concentration of a chemical in air to which exposure for a specific length
of time is expected to cause death in 50% of a defined experimental animal
population. NIOSH REL--National Institute of Occupational Safety and Health's
recommended exposure limit; NIOSH-recommended exposure limit for an 8-
or 10-h time-weighted-average exposure and/or ceiling.

The health and regulatory values cited in this factsheet were obtained
in December 1999.aHealth numbers are toxicological numbers
from animal testing or risk assessment values developed by EPA.
NIOSH and ACGIH numbers are advisory.bRegulatory numbers are values that have been
incorporated in Government regulations, while advisory numbers are nonregulatory
values provided by the Government or other groups as advice. NIOSH and
ACGIH numbers are advisory.

J.E. Amoore and E. Hautala. Odor as an aid to
chemical safety: Odor thresholds compared with threshold limit values
and volatilities for 214 industrial chemicals in air and water dilution.
Journal of Applied Toxicology, 3(6):272-290. 1983.

Agency for Toxic Substances and Disease Registry
(ATSDR). Toxicological Profile for Hexachlorocyclopentadiene.
Draft for Public Comment. Public Health Service, U.S. Department
of Health and Human Services. Atlanta, GA. 1997.

National Institute for Occupational Safety and
Health (NIOSH). Pocket
Guide to Chemical Hazards. U.S. Department of Health and
Human Services, Public Health Service, Centers for Disease Control and
Prevention. Cincinnati, OH. 1997.